Method of forming plutonium-bearing carrier precipitates and washing same



United States Patent 4 e IVIETHOD F FORMING PLUTONIUM-BEARING CARRIER PRECIPITATES AND WASHING SAME "Burt F. Faris, Richland, Wash, assignor to the United No Drawing. Application June 7, 1945 Serial No. 598,207

11 Claims. (Cl. 23-145) This invention relates gene ally to a procedure for processing of materials containing the element of atomic number 94, known as plutonium, for separating the plutonium from extraneous matter such as substance of the kind present in neutron irradiated uranium exemplified by uranium and especially fission products, and the like radioactive contaminants. More particularly, this invention concerns certain operations in a separatory and concentration procedure involving the use of a fluoride type of carrier wherein improved procedure is employed in treating the carrier containing the Pu.

As described herein, the isotope of element 94 having a mass of 239 is referred to as 94 and is also called plutonium, symbol Pu. In addition, the isotope of element 93 having a mass of 239 is Feferred to as 93 Reference herein to any of the elements is to be understood as denoting the element generically, whetherin its free state or in the form of a compound, unless indicated otherwise by the context.

Elements 93 and 94 may be obtained from uranium by various processes which do not form a part of the present invention including irradiation of uranium with neutrons from any suitable neutron source, but preferably the neutrons used are obtained from a chain reaction of neutrons with uranium. V

Naturally occurring uranium contains a major portion U a minor portion of U and small amounts of other substances such as UX and UX When a mass of such uranium is subjected to neutron irradiation, particularly with neutrons 'of resonance or thermal energies, U by capture of a neutron becomes U "irradiated uranium contains both 93 and 94 but by storing such irradiated uranium for a suitable period of time, the 93 is converted almost entirely to 94 In addition to the above-mentioned reaction, the reaction of neutrons with fissionable nuclei such asthe nucleus of U results in the production of a large number of radioactive fission products. As it is undesirable to produce a large concentration of these fission products which must,-i n view of their high'radioactivity, be separated from the 94 and further as the weight of radioactive fission products present inneutron irradiated uranium is proportional to the amounts of 93 and 94 formed therein, it is preferable to discontinue the irradiation of the uranium by neutrons when the combined amount of 93 and 94 'is equal-to approximately 0.02 percent by weight of the uranium mass.

As this concentration of these substances, the concentration of fission elements which must be removed is approximately the same percentage.

A number of processes have already been proposed for accomplishing the separation and concentration of- Pu. Certain of these processes are generically known as the bismuth phosphate type' process and the wet fluoride 2,875,022 Patented Feb. 24, 1959 ice type of process. These processes are the invention of others and the details of the processes are described in copending applications as for example application Ser. No. 519,714, now Patent No. 2,785,951, issued March 17, 1957, to be referred to hereinafter, which gives details relative to the aforementioned processes. Consequently, all of the details of operation of the aforementioned processes are not described herein.

In one type of procedure in successful use it is customary to utilize both the bismuth phosphate treatment and the lanthanum fluoride treatment. Consequently, the bismuth phosphate treatment is referred to herein for background although the present invention is concerned particularly with the treatment of the fluoride type of carrier precipitates. That is, the present invention concerns the treatment of the fluoride type of precipitates, exemplified by lanthanum fluoride precipitates carrying Pu, or other fluoride materialssuch as potassium plutonium fluoride. In processes of the aforementioned type, either combination processes where several diiferent types of carriers are used in which a fluoride carrier precipitation is accomplished in at least one of the steps,

or processes wherein fluoride compounds are more or less directly precipitated, these fluoride precipitates carrying Pu or comprising a fluoride compound of Pu are redissolved and subjected to further treatments such as the precipitation of Pu as the peroxide. In existing processes prior to the prose t invention, this peroxide precipitation step has involved certain difliculties. For example, some of the Pu is found in the supernatant liquid associated with the peroxide precipitate. Also, certain impurities or undesired components such as iron and rare earths have carried into the lanthanum fluoride carrier and have subsequently gone into solution when this carrier has been redissolved so that the plutonium containing liquid in which the peroxide precipitate has been formed contained these contaminants. Iron as a contaminant may be objectionable from the standpoint that it accelerates the decomposition of peroxide or otherwise presents difliculties and may be a contributing factor to Pu remaining in the supernatant liquid as above-mentioned.

The redissolving, aforementioned, of fluoride carrier is accomplished by a procedure termed metathesis, and briefly may comprise the following: The plutoniumcarrying lanthanumfluoride precipitate is treated in a suitable vessel byadding several volumes of 10 to 15 percent KOH or NaOH solution thereto and maintaining the resulting slurry between about 50 C. and C. for a period of 1-2 hours. Exchange of hydroxyl ions for fluoride ions of the lanthanum fluoride occurs to form an insoluble lanthanum hydroxide which carries the plutonium, while the fluoride ions go into solution. The metathesized material is separated from the solution and is carefully washed with water to remove fluoride ion therefrom as completely as possible. Alternatively, the plutonium-carrying lanthanum fluoride I precipitate may be metathesized with a solution of potassium carbonate. For example, 45 volumes in two steps of addition of a 45 to 50 percent solution of potassium carbonate may be added to a vessel containing the lanthanum fluoride precipitate and the resultant slurry maintained at a temperature of C. to 75 C. for a period of about 1 to 2 hours. The lanthanum fluoride precipitate dissolves in the potassium carbonate solution. The resulting solution is made 15% in KOH by adding 40% solution of KOH or NaOH to form a lanthanum hydroxide precipitate which also carries the plutonium.- This precipitate is separated as by centrifugation and is carefully washed to remove fluoride ion. The'washed fluoridefree materials resulting from either of the foregoing metathesis procedures may be treated with dilute nitric acid or: other suitable solvent or additions to yield a solution upon which a peroxide precipitation may be carried out.

The particular type of metathesis employed is not a limitation on the present invention and constitutes the work of others. 7 p

In accordance with the present invention I have found that by washing these fluoride precipitates by a procedure which will be described in detail hereinafter, prior to the metathesis of such precipitates that improved results may be obtained in later operations. For example, one improved result is that diversion of Pu by its remaining in the supernatant liquid associated with the plutonium peroxide precipitate is greatly reduced. Also, it has been found that the washing procedure of tl 1e present invention eliminates iron and certainother impurities or'contaminants thereby obviating the'possible difliculties of peroxide decomposition as well as assisting in the ultimate production of a purer and better quality final plutonium product. While water washes heretofore used may still be used, the washing of the present invention may be used in lieu thereof or supplemental thereto as may be preferred under the particular conditions prevailing in anycase. I, 7

That is, by the present invention which may utilize the same steps which have been previously used, but supple-'- mented and altered in certain respects the advantage of improved plutonium recovery may be obtained as will be described.

The meaning'of the terms bismuth phosphate type ofv process, wet fluoride type of process, product precipitate, and similar terms will be apparent as the description proceeds. This invention has for one object, to provide improvements in methods for. the separation and recovery of plutonium.

Another object is to provide a method of separating plutonium by a procedure characterized in that in certain steps difierent reagents and procedure than have heretofore been used are employed.

Still another object is to provide a procedure for washing fluoride compounds carrying or otherwise containing Pu.

Still another object is to provide a procedure for washing fluoride carrier precipitates containing Pu which also contain certain impurities.

A still further object is to provide a process for the washing of fluoride materials containing Pu which may be used in place of or in conjunction with usual washing processes. 7 p

Still another object is to provide certain new and mproved washing operations which lend'themselves to the use of and to coupling with steps already known or practiced for the separation and recovery of Pu.

I Another object is to provide a washing process which may be used in existing processes and which may be carried out in existing equipment without'change.

Still another object is to provide a washing process which may be applied to fluoride precipitates containing Pu either in relative small or large'amounts.

Still another object is to provide a method of ultimately obtaining an acid solution of certafn fluoride materials relatively free of iron and other impurities.

Other objects will appear hereinafter.

As pointed out above this invention relates toa process for'washing precipitates as exemplified'by lanthanum uoride containing Pu preferably prior'to the metathesis thereof. In present practice, in the concentration step-it iscustomary to apply a lanthanumv fluoride precipitation treatment prior to precipitating the Pu as the peroxide. The precipitation of'the'peroxide may not-in some instances, be particularly eflicient because some-ofthe Pu hasj'remlairled in the supernatant-liquid associated with e Pero i p ec p te. I 1 Therefore in accordance with the presentinventionythe Q directly made by an addition of H 0 4 lanthanum fluoride precipitate carrying Pu is washed with the solution of an acid salt. For example, it has been found that 2 to 10% solutions of an alkali hydrogen sulfate, such as NaHSO or KHSO or 'KH PO constitutes satisfactory wash solutions. Apparently these wash solutions cons'titutsolvents for contaminants carried; along in the lanthanum fluoride precipitation. That is, it has been found that the content of thelron contaminant accompanying the lanthanum fluoride precipitate is apparently washed out by washing in accordance with the present invention. Likewise, it appears that certain rare earth contaminants are also washed out. The lanthanum fluoride precipitate carrying Pu after being washed with the acid salt solution of the preseut invention may then 'be subjected to standard metathesis and the resultant lanthanum nitrate solution containing Pu may be subjected to a standard peroxide precipitationwith improved results. For example, in a peroxide precipitation applied to materials resulting from unwashed precipitate there was a diversion of product of approximately 2300 mg./l. of Pu in the supernatant liquid. On the other hand, in the case of similar materials which have been subjected to washing in accordance with the present invention, the diversion amounted to only about 40 mg./l.

A still further understanding of my invention may be had from a consideration of the following specific examples:

Example I In this example the precipitates treated comprised Ianthanum fluoride carrier containing about 7.5 mg. of plutonium. One precipitate was processed in a usual manner by metathesizing with a 40% carbonate solution." This gave solution containing plutonium, about 37.5 mg of lanthanum and was 1 N in nitric acid. The solution was adjusted to .2 N in sulfuric acid, the total'volumeof solution being one cc. A peroxide precipitation was However, -the greater part of the PuO decomposed.

The other portion of the sample, prior to metathesis, was first washed 30 minutes in accordance with the procedure of the present invention. That is, this sample was treated with 20 cc. of 10% potassium 'hydrogensulfate. The resulting lanthanum fluoride was then metathesized with 40% carbonate as in the treatment of the first portion of the sample. The resultant solution contained Pu to the extent of about 7.5 mg. was 1 N in nitric acid and .2 N in sulfuric as already described, the total volume of solution being 1 cc. 7

Peroxide precipitation was made at 60 C. followed by two hours digestion as above. In this run where the fluoride precipitate had been previously washed, the diversion of Pu was of the order of only about 100 mg.

per liter which indicated considerably smaller peroxide decomposition. 7

Example 11 In this example the lanthanum fluoride precipitate treated was substantially similar to that described in the preceding example; i The precipitate was washed with a 10% potassium hydrogen sulfate wash solution but the wash solution was also 1 N in HF. About 20 cc. of this wash solution was employed, and the washing was conducted for one hour at a temperature of C. The wash solution was separated from the precipitate by cen.- trifuging and analyzed. This spent wash solutionwas found to contain only 0.0042 mg. of Pu which can be considered a negligible loss in the efiiuent solution.

Example III In accordance with this-example, further runs were made to evaluate Pu losses in washsolutions containing "difierent-fluoride contents.-

In-these-runs a..3l8 g. sampleo-f'lanthanumfiuoride A containing 8 mg. of Pu was divided intofour "equal poi-- tions,'-and each portion washed'with 10 ccrof 'a solution comprised of potassium hydrogen sulfate and HF'as indicated in the table below: The washing was carried out for 'one hour at 75 C. The wash precipitate was separated from the washing solution by centrifugation and the separated spent wash solution analyzed. Th results of this' analysis were as follows:

Mg. (A) KHSO -NoI-IF 0.446 (B) 10% KHSO --1 N HF 0.060 (C) 10% KHSfO4--0.25 N HF 0.0275 (D) 10% KHS0 -0.5 N HF 0.05

tion. Also solubility is a function of temperature, low' temperature washes being accompanied by lower product losses.

Example IV In this example runs were made to compare the improvement obtained by washing with the potassium acid sulfate wash of the present invention with, for example, the prior art procedure involving the addition of a sulfide in metathesis for the purpose of improving the later precipitation of the Pu as a peroxide. The lanthanum fluoride precipitates treated were the same type as commonly encountered in ordinary operation and were similar to those treated in the other examples.

In run (A) the lanthanum fluoride precipitate was processed by potassium carbonate metathesis. The metathesis product was water washed and then dissolved in nitric acid and the Pu precipitated by. treatment with peroxide for two hours at a temperature of 55-60 C. In other words, the peroxide precipitation in this run was in keeping with ordinary practice. The solubility of the Pu in the supernatant liquid associated with the peroxide precipitate was 7530 mg./l.

In run (B) the lanthanum fluoride precipitate was washed with 10% potassium hydrogen sulfate in accord ance with the present invention for one hour at 75 C. 'prior to metathesis. Then, the washed precipitate after separation of the wash liquid was giveri a carbonate metathesis as in run A. The metathesis product was water washed and dissolved and the Pu precipitated as a peroxide by H 0 addition for two hours at a temperature of about 55 and 60 C. exactly as in the preceding run. The solubility of the Pu in the supernatant liquid associated with the peroxide precipitate was only 38.7 mg./l.

In run (C) a lanthanum fluoride precipitate of the same type was given a carbonate metathesis as in the preceding run. However, in this run a sulfide was added in accordance with prior practice, namely (NHQ S was added to the carbonate solution to the extent of .05 M. The iron sulfide was removed by .centrifuging. Then the water washed metathesized product was dissolved in nitric acid, and the other details of operation described above were carried out. The peroxide was precipitated and as in the preceding runs, the Pu in the supernatant liquid associated with the peroxide precipitate determined for comparison. The diversion of Pu content was 80 mg./l. in this run.

In run (D) a lanthanum fluoride precipitate was washed with potassium hydrogen sulfate as in run (B). A carbonate assisted KOH metathesiswas applied and the resultant metathesized water-washed product dissolved in' 1 N nitric acid and the otherusual steps applied. Likewise, peroxide precipitation as in the previous runs was made. Analysis indicated loss of Pu in the supernatant liquid associated with the peroxide precipitate was 90.1 mg./l. in this run.

fit)

This example concerns the evaluation of NaH PO as a wash for LaF as an alternative washing medium in accordance with the present invention. It was also desir able to have a wash that would involve low corrosion, hence, NaH PO was evaluatedas a supplement or substitute for KHSO A lanthanum fluoride precipitate of the type already described was washed with 10% NaH PO for 1 hour at C., centrifuged, and the LaF metathesized with K CO assisted KOH. After water washing and otherwise carrying out the other detailsof metathesis the water-washed precipitate was dissolved in 1 N HNO 0 give a solution containing 37.5 g./l. of La containing Pu. PuO was precipitated in the usual manner and the solubility determined. The diversion of Pu was found to be 990 mg./l. This was not quite as good as a KHSO wash, but showed a definite improvement over ordinary practice in comparison with the control of Example 1.

Example VI This example concerns evaluation of KHSO washing in the cold.

A .318 g. LaF product sample of the usual type, was used in each of the several runs. Twenty-five cc. of KHSO wash solution was used to slurry the precipitate and the slurry was allowed to stand for 30 minutes. Thereafter the slurry was centrifuged, and the separated precipitate metathesized by the carbonate assisted-KOH procedure as previously outlined. Each sample was made into a 6 cc. solution which was 1 N in HNO and .2 N in H 804. The analytical results showed that heating is not required, that 5% KHSO appears to be a very satisfactory concentration, and the presence-of HF in the wash solution does not interfere with the purification and does assist in preventing loss of Pu in the effluent washing medium.

All precipitations were carried out for 2 hrs. at 60 C. as in preceding examples. The loss of Pu product in the efiiuent wash was not over 1.8%.

The results of these several runs are summarized below:

From the foregoing it may be seen that it has been found that slurrying of precipitates containing Pu with wash solutions comprising acid salts, and also preferably containing a small amount of HF, at either room temperatures or higher temperatures, prior to redissolving such precipitates results in solutions from which appreciably improved yields of Pu may be obtained in subsequent Pu peroxide precipitation. Satisfactory conditions comprise the use of about 25 cc. of the wash solution for each .3 g. of precipitate containing Pu. That is,

wash solutions approximately 5% in the acid salt and .l N in HF are satisfactory. Satisfactory slurrying time is about 30 minutes at room temperature followed by separating the washed precipitate either by centrifuging or settling, followed by redissolving the washed precipi- 7 tate. 'lhe procedure is particularly applicable to fluoride COlIItfllDlllg carrier precipitates such as lanthanum fluoride .carrynig Pu on which the washing is applied prior to the metathesis of lanthanum fluoride precipitate. Any of the customary 'metathesis procedures for lanthanum fluoride precipitates may be applied to the washed precipitates of the present invention, and-there is considerable flexibility in this aspect.

Although it has been indicated that a wash solutron is satisfactory, this invention is not limited in this respect but wash solutions comprising from 2% to 15% of the'acid salt are also readily utilizable. Likewise the particular temperature at which the washing is carried out is not a limitation although for convenience washing at room temperature is preferred. The washing in ac cordance with the present invention may be in place of usual water washing or supplemental thereto and may be applied at one or more points in conjunction with the metathesis although the preferred operation is to wash prior to metathesis, thereby washing out and eliminating such impurities as iron and rare earth at the onset. The sodium and potassium derivatives of the salts have been described since they are common commercial compounds readily available. However the use of less familiar acid salts is not precluded providing that suitable washing and purification is accomplished as has been described.

It is to be understood that all'matter contained in the above description and examples shall be interpreted as illustrative and not limitative of the scope of this inventron, and it is intended to claim the present invention as broadly as possible in view of the prior art.

I claim: I.

1. A process for the recovery of Pu involving the segregation of the Pu in a LaF precipitate to he later followed by the dissolution thereof and thefurther prec pitation of the Puvas a peroxide, which comprises intlmat ely contacting the LaF precipitate with a 4%1 0% solution of sodium hydro-gen sulfate, said contacting being carried out at a temperature between C. to 95 C. for one-half to three hours, .separating the precip rtatefrom the effluent solution, redissolving the washed precipitate by metathesis, subjecting the solution contaming Pu resulting from said metathesis to the precipitat1on-of the Pu as a peroxide whereby the diversion of any l?u in the supernatant liquid associated with the peroxide precipitate is minimized. I

- In concentration processes for plutonium recovery which comprise the carrier precipitation of plutonium wherein a carrier for plutonium comprising a fluoride c'ompound is precipitated, andthe subsequent dissolution .and precipitation, as a peroxide, of plutonium carried thereby, the improvement which comprises washing the prec pitated, plutoniurn-bearing:carrier with an aqueous solut on of an alkali acid salt of a mineral acid, prior to said dissolution of plutonium.

In concentration processes :for plutonium recovery which comprise the.carrier precipitationof plutonium wherein a carrierfor plutonium comprising a fluoride compound is precipitated, and the subsequent dissolution and precipitation, as a peroxide, of plutonium carried thereby, theimprovement which comprises washing the "precipitated, plutonium-bearing carrier with an aqueous solution 'of a' salt comprising an alkalihydrogen sulfate,

prior to'said dissolution ofplutonium.

4. Inconcentration processes for plutonium recovery which comprise the carrier precipitation of plutonium wherein a carrier for plutonium comprisinglauthanum fluoride "is precipitated, and the subsequent dissolution and'precipitation, as a peroxide, c t-plutonium carried thereby,.the improvement which comprises washing the precipitated, plutonium-bearing carrier-with an aqueous s'olutron of analkali'acid salt of amineral :acid, prior 'to the saiddissolution'of plutonium.

V5. in concentration processes for the recovery ofv plutonium .from,so1utions containing the same together with dissolved iron contamination which comprise the carrier precipitation of plutonium together with said iron contamination wherein a carrier for plutonium compris-v ing lanthanum fluoride is precipitated, and the subsequent dissolution and precipitation, as a peroxide, of plutonium carried thereby, the improvement which comprises washing the precipitated, plutonium-bearing carrier with an aqueous. solution of a salt comprising an alkali hydrogen sulfate, prior to the said dissolution of plutonium.

6. In concentration processes for plutomum recovery which comprises the carrier precipitation of plutonium wherein a carrier for plutonium comprising lanthanum fluoride is precipitated, and the subsequent dissolution and precipitation, as a peroxide, of plutonium carried thereby, the improvement which comprises washing the precipitated, plutonium-bearing carrier with an aqueous solution of a salt comprising an alkali dihydrogen phosphate, prior to the said dissolution of plutonium.

7. In concentration processes for plutonium recovery which comprise the carrier precipitation of plutonium wherein a carrier for plutonium comprising lanthanum fluoride-is precipitated, and the subsequent dissolution and precipitation, as a peroxide, of plutonium carried thereby, the improvement which comprises washing the precipitated, plutonium-bearing carrier with a 2%l5% aqueous solution of potassium hydrogen sulfate, prior to the said dissolution of plutonium.

' 8 In concentration processes for plutonium recovery which comprise the carrier precipitation of plutonium wherein a carrier for plutonium comprising lanthanum fluoride is precipitated, and the subsequent dissolution and precipitation, as a peroxide, of plutoniumcarried thereby, the improvement which comprises washing the precipitated, plutonium-bearing carrier with a 2%l5% aqueous solution of sodium hydrogen sulfate prior to the saiddissolution of plutonium.

9. In concentration processes for plutonium recovery which comprise the carrier precipitation of plutonium wherein a carrier for plutonium comprising lanthanum fluoride is precipitated, and the subsequent dissolution and precipitation, as a peroxide, of plutonium carried thereby, the improvement which comprises washing the 'which comprise the carrier precipitation of plutonium fluoride is precipitated, and the subsequent dissolution wherein a carrier for plutonium comprising lanthanum and precipitation, as a peroxide, of plutonium-carried thereby, the improvement which comprises washing the precipitated, plutonium-bearing carrier with an aqueous solution of an alkali hydrogen sulfate containing hydrofluoric acid, prior to the said dissolution of plutonium.

11. In concentration processes for plutonium recovery which comprise the carrier precipitation of plutonium wherein a carrier for plutonium comprising lanthanum fluoride is precipitated, and the subsequent dissolution and precipitation, as a peroxide, of plutonium carried thereby, the improvement which comprises washing the precipitated, plutonium-bearing carrier with a 2%l5% aqueous solution of an alkali hydrogen sulfate of .fractional normality in hydrofluoric acid, prior to thesaid dissolution of plutonium.

References Cited in the file of this patent UNITED STATES PATENTS Binns Nov. 5, 1 935 

2. IN CONCENTRATION PROCESSES FOR PLUTONIUM RECOVERY WHICH COMPRISE THE CARRIER PRECIPITATION OF PLUTONIUM WHEREIN A CARRIER FOR PLUTONIUM COMPRISING A FLUORIDE COMPOUND IS PRECIPITATED, AND THE SUBSEQUENT DISSOLUTION AND PRECIPITATION, AS A PEROXIDE, OF PLUTONIUM CARRIED THEREBY, THE IMPROVEMENT WHICH COMPRISES WASHING THE PRECIPITATED, PLUTONIUM-BEARING CARRIER WITH AN AQUEOUS SOLUTION OF AN ALKALI ACID SALT OF A MINERAL ACID, PRIOR TO SAID DISSOLUTION OF PLUTONIUM. 